This application is based on patent application No. 10-153108 filed in Japan, the contents of which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to a printed circuit board testing apparatus for testing open circuit and current leakage or conductivity of a circuits pattern formed on a printed circuit board.
2. Discussion of the Related Art
A circuit board testing apparatus is disclosed, for example, in Japanese Unexamined Patent Publication No. (Hei) 5-73149 and Japanese Unexamined Patent Publication (Hei) 6-118115. In such circuit board testing apparatus, a circuit pattern on a circuit board is tested by the process of loading the circuit board on a transfer table, moving the transfer table to a position under a test head, and then lowering the test head to the transfer table to thereby allow contacts, such as checker pins or probe pins, attached on the test head to come into contact with specified positions of the circuit pattern formed on the circuit board. When the circuit board is placed at a designed position on the transfer table, and the transfer table is moved to the target position below the test head, the contacts provided on the test head come into the designed positional relationship with the circuit pattern of the circuit board, thereby assuring correct testing. However, it has been difficult practically to place a circuit board at the designed position on the transfer table.
The conventional circuit board testing apparatus is provided with a camera to pick up an image of a positioning mark provided on a circuit board to confirm a correct setting of the circuit board on the transfer table. Specifically, the amount of displacement of the circuit board with respect to the transfer table is calculated based on the thus-obtained mark image. In accordance with the calculated amount of displacement, the relative position of the test head and the transfer table is adjusted to compensate the displacement.
However, it is necessary to establish a correct positional relationship in advance between the transfer table carrying a circuit board and the test head provided with the contacts. In the conventional circuit board testing apparatus, a trial and error operation must be performed to determine the position of the camera until the positioning mark provided on the circuit board coincides with the optical axis of the camera, and render the contacts of the test head to come into the correct positional relationship with the circuit pattern on the circuit board.
Also, there has been proposed a circuit board testing apparatus which is provided with a test head having the so-called flying probes or movable contacts which move from one position to another position on a circuit pattern in accordance with a predetermined program to inspect a plurality of electrically conductive paths on the circuit board with a pair of the probes or contacts. The provision of movable contacts enables different types of circuit boards to be tested by the same test head. However, in such a type of testing apparatus, the number of contacts are limited. Accordingly, each of the contacts must come into contact with the circuit board an increased number of times, consequently the tip of each contact wears off in a short time. This requires frequent replacement of the contacts or the probes. At each replacement, it is necessary to adjust the positional relationship to ensure correct matching of the tip of a replaced contact with the specified position of the circuit pattern.
Further, recent circuit boards are formed with a more complicated circuit pattern. Accordingly, more precise positional control is required for the contact or probe to meet or come into contact with the specified position of the circuit pattern.
With the conventional circuit board testing apparatus, the adjustment of positional relationship between the contacts on the probes and a circuit board to be tested is performed manually by the operator. Accordingly, the more complicated the circuit pattern is, the more the load for the operator is, consequently lowering the operational efficiency for circuit board testing. Further, the troublesome adjustment of the positional relationship between the test head and the circuit board carrier or the transfer table must be performed each time a test head is replaced with another because each test head has its own dimensional characteristic. Furthermore, even during the testing operation using the same test head, it has been necessary to adjust the position of the positioning mark image pick-up camera at a specified interval. This is because the relative position between the camera (or the test head) and the transfer table changes with repeated testing operations, possibly lowering the accuracy of the test. Accordingly, the operator is required to carry out the troublesome adjustment of the positional relationship or the camera position frequently, thus resulting in a tremendous load for the operator.
It is an object of the present invention to provide a circuit board testing apparatus and method which are free from the problems residing in the prior art.
It is another object of the present invention to provide a circuit board testing apparatus that enables precise positioning of a circuit board relative to test probes or contacts.
It is further object of the present invention to provide a circuit board testing apparatus which can be easily operated but ensures precise control of the relative positions of the test head and a circuit board to be tested.
It is another object of the present invention to provide a circuit board testing apparatus which automatically determines and adjusts relative position of a circuit board to be tested and a test head or test probes carried thereon.
It is a still further object of the present invention to provide a method of automatically determining and adjusting the relative position of a circuit board to be tested and a test head or test probes carried thereon.
In one aspect of the present invention, a printed circuit board testing apparatus includes a first measuring system for determining a relative position between a circuit board carrying table and a test head with respect to two dimensions and an angular direction, a second measuring system for determining a relative position between the table and a circuit board carried by the table with respect to two dimensions and an angular direction, and a drive system for bringing the table and test head into a first relative positional relationship for the testing of the circuit board in accordance with the relative positions determined by the first and second measuring systems.
In another aspect of the present invention, a method for adjusting the relative position of a circuit board to be tested and a test head, includes determining a relative positional relationship between a circuit board carrying table and a test head with respect to two dimensions and an angular direction; determining a relative positional relationship between the table and the circuit board carried by the table. The table and the test head are moved in accordance with the determined relative positional relationships.
According to an embodiment of the present invention, the circuit board carrying table is movable in a first direction as identified by the Y direction, for example. The drive system first transports the table to a predetermined position relative to the test head. The first measuring system determines the positions of two points on the test head relative to a particular point of the table at the second relative positional relationship. The drive system drives the test head in the Y direction, in a second direction perpendicular to the Y direction and referred to as X direction by for example in the embodiment, and in angular direction. An adjusting mechanism controls a test head driving mechanism to adjust the positional relationship of the test head with the table such that the test head is in parallel with the table.
In an embodiment, the relative position between the particular point on the table and the two points on the test head may be identified by coordinates in a coordinate system with x and y axes extending in the X and Y directions with its origin being coincident with the particular point on the table. The test head driving mechanism adjusts the position of the test head in accordance with the x and y coordinates of the two points on the test head such that the y coordinates of the two points become equal to each other. Then, the table is returned back to an initial or preparatory position where a circuit board to be tested is mounted. The table carrying the circuit board is transported to a testing position in accordance with the y coordinates of the two points of the test head at the adjusted position. The test head may be driven in X direction in accordance with the x coordinates. The data determined by the second measuring system are used to correct or compensate the amount of movement of the table and the test head.
In the embodiment of the present invention, the first measuring system includes a mechanism to bring the table and the test head into a first, second and third relative positional relationship. The positions of the two points on the test head are determined as a function of the relative movement of the table and the test head from the first, second, and third relative positional relationships. The first, second and third relative positional relationships may be determined by target marks fixed on them and an image taking device such as camera.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.